1. Field of the Invention
This invention relates to a method of making brake pads and the like from a brake friction material.
2. Background Art
Brake pads, and for that matter brake shoes or liners, are usually formed from a blend of friction materials and binders; the blend is first proportioned, and then heated and pressed in specially provided molds to make it fast with metal supports or plates, possibly after a suitable clinging substrate has been interposed between the friction material blend and the metal support.
In an effort to raise the output, specifically by reducing the time required for hot-pressing through the molding press--on which time the production rate is largely dependent--conventional methods have provided for a pre-heating step of the friction material dosages. In fact, with such a pre-heating step, the hot-press molding machine operation time could be cut down by up to 50% with some friction material blend types.
Conventional methods provide for pre-compacting, where feasible by a cold process, the brake pad friction material dosages within specially provided mold cavities, followed by placement of the pre-compacted dosages on a tray. Thereafter, the tray is preheated and taken manually, along with the heated dosages thereon, to the molding machine, the metal supports are positioned, and a final hot-molding step is completed.
Such conventional methods have the well-recognized disadvantage of yielding occasionally a non-uniform product, because if the friction material is not properly metered into the mold cavities and the pre-compacted dosages are not all exactly of the same weight, the molding machine is apt to apply different pressures to the various dosages since it acts over a common pressure plane for all the mold cavities.
Note is made, moreover, that ahead of the final molding step, the friction material dosages would not yet be sufficiently coherent to permit of convenient handling.
In addition, where the friction material is compounded of such materials as Kevlar, glass fiber, or some other constituents of the most commonly used fibrous compositions based on asbestos, difficulties are experienced during the initial brake pad-making steps, also because such compositions cannot be effectively pre-compacted by a cold process.
Lastly, since the operations involved are to be largely carried out manually, keeping a close control of the pre-heating and molding machine residence times is difficult with conventional methods. More or less conspicuous variations in these times may result in significant alterations of the quality levels of the brake pads obtained.